by James A. Bacon
A Duke University study of coal ash has found that the mineral residue from coal combustion contains high concentrations of valuable rare-earth elements neodymium, europium, terbium, dysprosium, yttrium and erbium used in uses as varied as cell phones, rechargeable batteries, fluorescent lighting, air pollution controls, and night-vision goggles.
Demand for the exotic elements has exploded in recent years. While no rarer than metals such as chromium, nickel or zinc in the earth’s surface, they are rarely found in extractable concentrations. In 2010 China, which produced 95% of the world’s supply of rare earth elements, restricted exports, sending prices shooting higher and prompting a search for alternate sources of supply.
“The Department of Energy is investing $20 million into research on extraction technologies for coal wastes, and there is literally billions of dollars’ worth of rare earth elements contained in our nation’s coal ash,” said Heileen Hsu-Kim, a professor of civil and environmental engineering at Duke, as quoted in Science Daily.
Researchers studied coal ash samples from power plants located mostly in the Midwest that burn coal sources from all over the country. Analysis showed that ash collected from the Appalachian Mountains has the highest concentration of rare earth elements at 591 parts per billion. However, Appalachian ash is harder to extract, perhaps because it is more likely to be encapsulated within a glassy matrix of aluminum silicates.
“The reagents we used are probably too expensive to use on an industrial scale, but there are many similar chemicals,” said Hsu-Kim. “The trick will be exploring our options and developing technologies to drive the costs down. That way we can tap into this vast resource that is currently just sitting around in disposal ponds.”
Bacon’s bottom line: The next big environmental debate over coal ash is over how to dispose of the ash once it is de-watered. Dominion Virginia Power and many other power companies say it is cheaper to consolidate the material in compounds capped to prevent rainwater from percolating through. But environmentalists would like to see the coal ash disposed in landfills with heavy plastic lining that eliminates any risk of groundwater contamination.
Will the Duke University finding change power company calculations? If a given power station’s coal ash potentially contained a hundred million dollars worth of rare earth metals, would a power company be more likely to hang on to the material for future extraction? Who knows — the world works in strange and unpredictable ways.
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